October 12, 2022
Visualizing and Manipulating Chiral Edge States in a Moiré Quantum Anomalous Hall
Quantum anomalous Hall (QAH) insulators are topological phases of matter that host one-dimensional chiral edge states that conduct electric current unidirectionally, thus leading to quantized Hall conductance and dissipationless carrier transport. We have used scanning tunneling microscopy and spectroscopy to visualize and manipulate chiral edge states in a moiré QAH insulator made from twisted monolayer-bilayer graphene. We observe local spectroscopic signatures for correlated insulating states having total Chern numberCtot = ±2and have characterized their evolution in an out-of-plane magnetic field. We have determined the relationship between topological behavior and local twist angle accompanied by hetero-strain, and show that the sign ofCtotcan be controlled via electrostatic gating over a limited range of twist angles under a small strain. This enables the stabilization of domains having opposite Chern numbers and the visualization of chiral edge states residing at domain interfaces. Variation of carrier density via global back-gating enables controlled spatial displacement of edge states having fixed chirality. The formation of tip-induced quantum dots provides local control over the carrier density and Chern number, and thus enables the local creation of chiral edge states having reversible chirality.
Canxun Zhang is a Ph.D. student working in Prof. Michael Crommie’s group, in the Physics Department at UC Berkeley. He received a BS in Physics from Peking University in 2017. Canxun’s research investigates the electronic properties of graphene and transition metal dichalcogenide (TMD) based moiré systems using scanning tunneling microscopy and spectroscopy (STM/STS).